214 research outputs found
Massive Gravitino Propagator in Maximally Symmetric Spaces and Fermions in dS/CFT
We extend the method of calculation of propagators in maximally symmetric
spaces (Minkowski, dS, AdS and their Euclidean versions) in terms of intrinsic
geometric objects to the case of massive spin 3/2 field. We obtain the
propagator for arbitrary space-time dimension and mass in terms of Heun's
function, which is a generalization of the hypergeometric function appearing in
the case of other spins. As an application of this result we calculate the
conformal dimension of the dual operator in the recently proposed dS/CFT
correspondence both for spin 3/2 and for spin 1/2. We find that, in agreement
with the expectation from analytic continuation from AdS, the conformal
dimension of the dual operator is {\it always} complex (i.e. it is complex for
every space-time dimension and value of the mass parameter). We comment on the
implications of this result for fermions in dS/CFT.Comment: 20 pages, references added, v3: typos fixe
Stability of D-brane embeddings in nontrivial backgrounds
We propose a new analytical method for determining whether nonsupersymmetric
probe branes embedded in nontrivial backgrounds are perturbatively stable or
not. The method is based on a relationship between zero mass solutions of the
relevant DBI equations of motion and tachyonic solutions. Furthermore, due to
the above relation, the question, of whether a classical solution is stable or
not, can be answered simply by studying the derivatives of that solution with
respect to its integration constants. Finally, we illustrate the efficiency of
this method by applying it to several interesting examples.Comment: 18 pages; introductory material added in Section 2, journal versio
On Non-slow Roll Inflationary Regimes
We summarize our work on constant roll inflationary models. It was understood
recently that constant roll inflation, in a regime beyond the slow roll
approximation, can give models that are in agreement with the observational
constraints. We describe a new class of constant roll inflationary models and
investigate the behavior of scalar perturbations in them. We also comment on
other non-slow roll regimes of inflation.Comment: 10 pages, contribution to the proceedings of the 10th International
Symposium "Quantum Theory and Symmetries", 201
On the Stability of D7 - anti-D7 Probes in Near-conformal Backgrounds
We investigate the perturbative stability of a nonsupersymmetric D7 - anti-D7
brane embedding in a particular class of type IIB backgrounds. These
backgrounds are the gravitational duals of certain strongly-coupled gauge
theories, that exhibit a nearly conformal regime (known as a walking regime).
Previous studies in the literature have led to conflicting results as to
whether the spectrum of fluctuations around the flavor D7 - anti-D7 embedding
has a tachyonic mode or not. Here we reconsider the problem with a new
analytical method and recover the previously obtained numerical results. We
also point out that the earlier treatments relied on a coordinate system, in
which it was not possible to take into account fluctuations of the point of
confluence of the D7 - anti-D7 branes. Using an improved coordinate system, we
confirm the presence of a normalizable tachyonic mode in this model, in
agreement with the numerical calculations. Finally, we comment on the
possibility of turning on worldvolume flux to stabilize the probe branes
configuration.Comment: 22 pages; explanations added, minor typos corrected, journal versio
Spinor two-point functions and Peierls bracket in de Sitter space
This paper studies spinor two-point functions for spin-1/2 and spin-3/2
fields in maximally symmetric spaces such as de Sitter spacetime, by using
intrinsic geometric objects. The Feynman, positive- and negative-frequency
Green functions are then obtained for these cases, from which we eventually
display the supercommutator and the Peierls bracket under such a setting in
two-component-spinor language.Comment: 22 pages, Latex. In the final version, the presentation has been
improve
Heterotic Flux Attractors
We find attractor equations describing moduli stabilization for heterotic
compactifications with generic SU(3)-structure. Complex structure and K\"ahler
moduli are treated on equal footing by using SU(3)xSU(3)-structure at
intermediate steps. All independent vacuum data, including VEVs of the
stabilized moduli, is encoded in a pair of generating functions that depend on
fluxes alone. We work out an explicit example that illustrates our methods.Comment: 37 pages, references and clarifications adde
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